1. Technical Field
This invention relates to gas turbine engines having convergent/divergent nozzles in general, and apparatus for sealing within nozzles in particular.
2. Background Information
An exhaust nozzle provides a means for optimizing thrust produced within a gas turbine engine. In augmented gas turbine engines, convergent/divergent (CID) nozzles are particularly favored because of the multitude of nozzle positions possible. Flaps circumferentially distributed aft of the augmentor form the convergent and divergent sections for which the nozzle is named. Flap seals disposed between adjacent flaps minimize gas leakage between flaps in both sections. The convergent section is pivotally connected to the augmentor and to the divergent section. The divergent section is pivotally connected to the convergent section and to an external fairing positioned radially outside of the divergent section. The opposite end of the external fairing is pivotally attached to a static outer casing which surrounds a portion of the nozzle. Together, the outer casing, the convergent and divergent sections, and the external fairing form a plenum hereinafter referred to as the xe2x80x9cnozzle plenumxe2x80x9d.
Because of the high temperature of the core gas exiting the turbine and augmentor, nozzles are cooled with air bled off of the fan at a lower temperature and a higher pressure than that of the core gas flow passing through the nozzle. Cooling air enters the core gas path within the augmentor via cooling holes in the augmentor liner and subsequently passes into the nozzle as a layer of cooling air traveling along the surface of the nozzle flaps and flap seals. Cooling air within the nozzle plenum cools the opposite side of the flaps and flap seals.
One significant disadvantage of this approach is that the layer of cooling air traveling along the augmentor liner and nozzle increases in temperature as a function of distance traveled. At the same time the temperature increases, the geometry of the layer erodes and further inhibits the ability of the cooling air layer to thermally protect the adjacent augmentor or nozzle component. As a result, adequate cooling air flow for the convergent section may be insufficient for the divergent section. If the cooling air flow is increased to meet the minimum required for the divergent section, an excessive amount would be used to cool the convergent section. A person of skill in the art will recognize that it is a distinct advantage to minimize the amount of bled cooling air used within a gas turbine engine.
To avoid the above described problems, some applications employ cooling air ejectors disposed in the divergent flaps and flap seals. Cooling air from the nozzle plenum passes through the ejectors and either forms a new layer, or augments an existing layer, traveling aft over the divergent flaps and flap seals. This approach improves the cooling layer performance along the divergent section. A problem with this approach, however, is that the cooling air initially produced as fan bypass air encounters numerous pressure drops within the bypass air plenum as it travels aft from the fan to the nozzle. One of the more significant drops occurs in the nozzle plenum, where the cooling air is directed toward the joint between the divergent section and the external fairing.
What is needed is a nozzle that provides adequate cooling for both the convergent and divergent sections and one that uses minimal cooling air.
It is, therefore, an object of the present invention to provide a nozzle that requires minimal cooling air.
It is another object of the present invention to provide a nozzle that adequately cools the divergent flaps and flap seals.
It is still another object of the present invention to provide a sealing apparatus for a nozzle that is effective for multiple nozzle positions.
It is still another object of the present invention to provide a sealing apparatus that is easily manufactured and implemented.
According to the present invention, a nozzle for a gas turbine engine is provided which includes an outer casing, a convergent section, a divergent section, an external fairing, and a collapsible seal member. The divergent section has an aft end and a forward end, and the forward end of the divergent section is pivotally attached to the convergent section. The external fairing has an aft end and a forward end. The forward end of the external fairing is pivotally attached to the outer casing and the aft end of the external fairing is pivotally attached to the aft end of the divergent section. The external fairing is disposed radially outside of the divergent section. The collapsible seal member extends between the outer casing and the divergent section, circumferentially around and outside of the divergent section.
According to one aspect of the present invention, the divergent section includes a plurality of ejector slots through which cooling air may pass. The ejector slots are oriented such that cooling air may pass from the nozzle plenum, through the divergent section, and travel along the surface of the flap as a layer before mixing with the passing core gas flow.
An advantage of the present invention is that it minimizes the volume of cooling air necessary to adequately cool the divergent section of the nozzle. A person of skill in the art will recognize that nozzles having flaps and flap seals are notorious for cooling air leakage. The present invention nozzle, which includes the collapsible seal, limits cooling air leakage within the nozzle plenum, and thereby minimizes the total volume of cooling air necessary. The present invention also minimizes the cooling air volume requirement by enabling the divergent section to be cooled more efficiently. The embodiment using the collapsible seal in combination with the ejector slots in the divergent section avoids having to provide excessive cooling in the convergent section to insure adequate cooling in the divergent section.
Another advantage of the present invention is that it minimizes the amount of work required to provide cooling air to ejector openings disposed in the divergent section. The collapsible seal portion of the present invention minimizes cooling air pressure losses between the fan and the divergent section thereby minimizing the amount of work required to provide the cooling air. A person of skill in the art will recognize that work required to increase the pressure of the cooling air does not add to the thrust of the engine and therefore decreases the efficiency of the engine.
These and other objects, features and advantages of the present invention will become apparent in light of the detailed description of the best mode embodiment thereof, as illustrated in the accompanying drawings.